1. Field of the Invention
The present invention is directed to a method for the production of a light conductor structure which has an electrode arranged between the light conductors.
2. Prior Art
Light conducting structures, which have a pair of light conductors with electrodes disposed therebetween, are known. Such structures are used as electrically controllable directional couplers in optical communication technology and act as switches or change-over switches. In addition, such structures are used as electro-optical modulators.
A common feature of these structures is that the two light conductors possess a zone in which they are very closely adjacent to one another. Electrodes are arranged in this zone between the light conductors and also beside each of the light conductors. In this zone a typical value for the spacing between the pair of light conductors is 3.mu.m. This means that the electrodes must be precisely adjusted in their position relative to the conductor and that permissible tolerances are less than 1.mu.m.
A switch, which can be used as the modulator and which comprises two coupled light conductors which can be detuned relative to one another by applying an electrical field to the conductors, is disclosed in an article by H. F. Taylor, "Optical Switching and Modulation in Parallel Dielectric Waveguides," J. Appl. Phys., Vol. 44, No. 7, July 1973, pp. 3257-3262.
If two light conductors are arranged so that they are closely adjacent over a sufficiently long path, they are optically coupled to one another. For example, in a coupling length L, a periodic exchange of optical energy takes place between the two conductors. If both light conductors are loss-free and their phases are matched to one another, the energy exchange is complete. If, however, the propagation constants for the light changes asymmetrically in the light conductors, only a part of the energy is exchanged. Furthermore, there is also a change in the coupling length L over which the maximum energy exchange will occur.
If the light conductors are produced from electro-optical material, it is possible to control the index of refraction and thus the propagation constants in the light conductors by applying an electrical field to the light conductors. The coupling strength, which is dependent upon the distance between the intercoupled light conductors, upon the refractive indices of the conductors, and the coupling length L, is selected to be such that when no electrical field is applied, the energy from one light conductor is coupled in full to the other light conductor. By applying the electrical field to the light conductors, the propagation constants of two light conductors are detuned relative to one another in such a manner that in a given coupling length L, a part of the optical energy is first coupled into the other light conductor and then it is coupled back again.
However, when a central electrode is arranged between the two light conductors, particular difficulties will occur. These difficulties are due to the fact that the distance between the coupled light conductors is only between 1 .mu.m and 3 .mu.m and due to the fact that the central electrode must be positioned as exactly as possible between the light conductors. Thus, tolerances for the position of the electrode are extremely small.